Roofing Calculator

Calculate shingles, underlayment, and ridge cap for gable roofs. Enter building dimensions and roof pitch — waste factor included.

Roofing material estimates start with two measurements: the building footprint and the roof pitch. The pitch multiplier converts a flat 2D footprint into the actual 3D surface area a roofer must cover. A 6:12 pitch, for example, increases surface area by about 11.8% over the footprint. This calculator applies the correct multiplier from IRC tables, then factors in your chosen waste percentage to produce bundle, underlayment, and ridge cap quantities suitable for a supplier quote.

Frequently Asked Questions

How do I measure roof pitch?

Place a level horizontally against the roof. Measure 12 inches along the level, then measure the vertical distance from that point down to the roof surface. That vertical measurement is your pitch expressed as X:12.

What waste factor should I use for roofing?

Use 10% for simple gable roofs. For hip roofs or roofs with many valleys and dormers, use 15%. Complex roofs with multiple penetrations may need 20%.

How many shingle bundles are in a square?

Most standard three-tab and architectural shingles require 3 bundles per square (100 sq ft). Some premium or specialty shingles may require 4 or 5 bundles — always verify with the manufacturer.

Does this calculator account for ridge vents?

The calculator estimates ridge cap bundles based on ridge length. Ridge vent material is separate — consult your ventilation manufacturer for the linear feet of ridge vent needed based on your attic square footage.

Estimates are for planning purposes only. Verify quantities with your supplier and confirm code requirements with your local building department.